BARNSTABLE — The Mendes murder case is set to take another step forward next week when one of the juvenile defendants heads for a court appearance in Plymouth.

Mykel Mendes, now 17, is set to appear in Plymouth Juvenile Court on Monday on charges that stem from the murder of his half-brother nearly five years ago, according to a source familiar with the case. Kevin Ribeiro, also 17, has a trial date set for Sept. 10.

Mykel Mendes and Ribeiro — both 13 at the time — along with Robert Vacher, 23, were charged in 2009 with the murder of 16-year-old Jordan Mendes in December 2008. The Cape and Islands District Attorney's Office, as well as attorneys for Ribeiro and Mykel Mendes, declined comment for this story.

Family members found Mendes' body smoldering in a pit off Jennifer Lane in Hyannis shortly before Christmas. He had been stabbed 27 times and shot in what prosecutors say was a robbery. The three defendants allegedly stole a large amount of oxycodone and about $10,000 in drug money from Jordan Mendes that they later used to buy a BMW.

Following a three-week trial in November 2011, a Barnstable Superior Court jury convicted Vacher of first-degree murder. His case is on appeal to the Massachusetts Appeals Court, according to court documents.

The two juvenile defendants were spared the same fate by three months.

According to state law, a juvenile offender convicted of committing an offense before his or her 14th birthday cannot be incarcerated on those charges beyond age 18. This means that even if convicted of murder, Ribeiro and Mykel Mendes face less than a year of prison time, although they have both been in custody since their arrest.

Before 2009, the state Department of Youth Services could hold a juvenile defendant after age 21 if it determined he or she was dangerous. The state Supreme Judicial Court overturned that ruling, citing questions of constitutionality in the law.

That isn't the first SJC ruling to apply to the teens' cases.

In April, the high court upheld a change-of-venue ruling from Barnstable Juvenile Court Judge James Torney, citing the significant pretrial publicity surrounding the case.

The district attorney's office had appealed the decision, arguing that the judge should have at least tried to empanel a jury before moving the trial.